melchiz: I'm surprised that Microsoft doesn't care about any of this. Many of us use Windows because we game. If Windows no longer is necessary for gaming, what will stop thousands of users from switching to Mac OS, Ubuntu, and so on?
Microsoft doesn't care because of one word: DirectX.
Microsoft's gaming dominance on Windows and the 360 owes a lot to DirectX. There are excellent development tools available for it, and projects can be moved between not only Windows and the 360 but also the Zune and Windows Phone 7. Porting to any of these platforms requires minimal effort compared to other platforms--all versions build from the same tree in Visual Studio, with common assets kept separate from platform-specific code.
Microsoft's latest presentation for Windows Phone 7 claims the platform game being demonstrated is 90% shared code. Being able to make a game for two or more platforms at once is a very attractive option, and the ease of use of the development environment has led to many developers treating the 360 as the lead platform, with some even releasing games only on the 360 and PC.
Contrary to popular belief the PS3 and Wii don't actually run true OpenGL, so implementing OpenGL doesn't actually allow a title to hit the PS3 and Wii in addition to OS X and Linux in the same manner that DirectX does with the Microsoft platforms. Additionally there is no SDK environment for OpenGL comparable to those for DirectX. OpenGL is just a renderer, so developers working with it also need to worry about what to use for sound and other functionality; DirectX is a comprehensive package.
The OS X/Linux install base is sufficient for indie titles, but for serious developers the increased development cost--because of the lack of tools--and insignificant user base simply isn't worth it.
